1. Field of the Invention
The following invention relates to sewing machines, and more particularly, to automatic apparatus for monitoring and controlling thread tensioning force in a sewing machine.
2. Description of Prior Art
An existing sewing machine routes the sewing thread through a tensioning apparatus and the thread tension is manually adjusted by an operator, in part, by means of a pair of discs that are compressed against the thread. The correct tension results in a stitch that looks identical on both sides of the material. That is, the knots of the stitches are pulled into the fabric and are no more visible on the top than on the bottom.
To tighten the thread feeding into the needle, a thread-tensioning knob on the front of the machine is turned through a range of about five revolutions to compress a spring that squeezes the two discs together. Generally, the tension must be looser when sewing thinner fabric and tighter when sewing thicker fabric. Further, thread type can affect tension. If the sewer is using rayon thread, the tension will have to be a little looser because the tensile strength of rayon is not the same as that of polyester. Polyester can stand a tighter tension and needs a tighter tension to avoid looping.
Proper tension adjustment will eliminate problems associated with loose threads, looping, puckering, bunching, and other like problems. The problems associated with proper thread tensioning are described in U.S. Pat. No. 6,152,057, “Bobbin Assembly Incorporating a Thread Tensioning Assembly and Method of Controlling the Payout of Thread From a Bobbin Assembly”, issuing Nov. 28, 2000 to Badillo, the Specification hereby incorporated by reference.
However, thread tensioning apparatus of the typical sewing machine does not provide any means of monitoring or measuring the compression force applied to the discs or the comparing of the thread tensioning force to a predetermined reference to assure that the proper thread tension is applied to the sewing thread.
There have been many proposals for automating the above-mentioned regulation of proper thread tension. However, practical and useful proposals have not been realized.